Discussion on Late Permian coal-accumulating environment and its coal-forming pattern in Laochang coalfield,eastern Yunnan Province,China

The authors comprehensively analyzed the geological background and the epositional characteristics of the Late Permian coal bearing strata in Laochang coalfield,eastern Yunnan.The typical coal accumulating environment and coal forming effects with the tidal flats and the deltas are discussed in details.Accordingly,it was recognized that sequence of the environmental evolves of the Late Permian strata in this area is :the confining carbonate platform—the lagoons and the tidal flats—the shallow water deltas of sea.The coordination of various conditions was most suitable to coal accumulating from the Middle Longtan stage to the Chanxing stage of the Late Permian.As a result,these tidal flats and these shallow water deltas of the Late Later stage Permian are the most important coal accumulating environments in this area.They formed numerous more stable and thicker coal seams.Based on this,The coal accumulating environment evolves and coal forming pattern of the coal accumulating stage of the Late Permian in this area was established primarily.